Traditionally, people mount a horse from the left side (although today, we train them to accept someone getting on them from both sides). I was always told that this was because knights used to wear their swords on their right leg, which they then had to keep straight when mounting. Thus, they bent their left leg into the stirrup and were able to swing their right leg over straight. However, recently I have noticed that whenever I see knights depicted in paintings or movies, the sword is typically on the left side. Can you help me figure this one out? What is the straight dope on why people traditionally mount horses on the left side?

— Heather Hipp, Atlanta, GA

We'd better begin by acknowledging the obvious, Heather. The fact is that most people don't mount a horse from the left side. Most people call a cab. Those having some acquaintance with horsemanship, however, know that the left side is the horse's "near" side while the right side is the "off" side. This is often explained in terms of swords, but we're then obliged to acknowledge obvious fact #2: While a fair number of people still ride horses, you're living in one tough neighborhood if you need to do so while wearing a sword.

About those swords. I'm afraid you've gotten the explanation a little scrambled. As you've observed, swords are traditionally worn on the left, since that makes it easier for a right-handed swordsman to pull the sword from its scabbard. If you're wearing a sword on the left, you'll want to mount your horse on its left, since otherwise the sword will get in the way. The practice goes way back before the medieval heyday of knights. In fact, it most likely originated when sword-toting warriors first began riding horses into battle.

The ancient Greek general Xenophon (c.430-c.355 B.C.), in his treatise The Art of Horsemanship, gives a step-by-step description--literally--of mounting a horse. Since the stirrup hadn't been invented yet (and wouldn't be until around 400 A.D.), this involved grasping the horse's mane in two places--up by the ears with the left hand and at the base of the neck with the right. The rider would then jump up while swinging his right leg over the horse's back (horses tended to be shorter in ancient times). Alternatively, if he was carrying a spear, the rider could use it to vault onto his charger. Xenophon advocates learning to mount from the right or "off" side in case the exigencies of war required it. It's plain from his detailed description that the left or "near" side of the horse was the correct side for mounting in Xenophon's time, when horses were primarily used for war.

Even when the stirrup came into use, the sheathed sword would still be in the way in mounting from the right, and would be likely to jab the horse in the side or rump just as the rider was swinging his leg over its back. The startled horse would then be strongly inclined to bolt, leaving the rider (briefly) in midair.

So why do we still mount from the left? After all, except for the occasional ceremony, the cavalry has ridden off into the sunset. To answer the question, we need to delve into equine physiology and psychology.

Let's start with a fundamental fact, essential to understanding equines: The horse isn't a predator--it's prey. Even after millennia of domestication, the horse is physically and mentally hardwired to detect and elude attackers. Its eyes are set on the sides of its head, giving it almost 360 degrees of vision. It sees two monocular fields at once, one through each eye. The binocular vision we human predators take for granted, the horse has in only a small area directly ahead of it. So what it "knows" on one side, it doesn't "know" on the other, until it's been shown. The horse's instincts dispose it to be suspicious of anything new in its environment. The thing behind that rock that wasn't there yesterday could be a lion!

What does this have to do with mounting from the left? It means that a horse who's been taught to accept being mounted only from one side may be perfectly docile when the rider clambers aboard on that side, yet spook and refuse to stand still if approached from the unfamiliar direction. That's why authorities on horse training (including our old friend Xenophon) recommend teaching horses to be mounted from the off side, so that they'll stand still for it if circumstances demand that the rider get on from that side

But why prefer the left side when swords are no longer a problem? Partly it's the inertia of tradition--horses and humans are both creatures of habit. But it's also common sense to have a standard approach. If you didn't know which side a particular horse had learned to be mounted from, you could get a nasty surprise if you tried to get on from the "wrong" side.

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